1. Field of the Invention
The present invention has to do with dispersible starch products and particularly relates to physically modified starch products prepared using pressure (shear) and heat such as in an extrusion process. The products of the invention have improved functionality in food applications, particularly in instantized hot or cold applications.
2. Description of Related Art
Starches are widely used in food applications as thickeners or bodying agents. They are unique among carbohydrates in occurring as discrete granules. In modern day food processing and storage applications, however, the properties of granular starch must be modified to withstand certain heat, acid and freeze-thaw conditions. Presently, food processors prefer to avoid chemically modified starches and employ natural products such as physically modified starches.
When granular starch is heated in excess water above the gelatinization temperature, it undergoes hydration and gelatinizes, forming a viscous solubilized paste. In practice, starch granules require dispersion in cold water before cooking at the time of use.
Pregelatinized starch products have been developed that provide reconstituted pastes when mixed with hot or cold water. The starch manufacturer hydrates the raw starch and then gelatinizes the starch by such techniques as roll-drying or spray-drying and the like. Unfortunately, the dried pregelatinized starch product does not readily disperse in hot water and agglomerated masses are formed giving lumpy pastes with inconsistent paste viscosities.
Attempts have been made to circumvent the dispersibility problem by inclusion of surfactants with dried pregelatinized starch and somewhat improved dispersibilities were obtained as exemplified in U.S. Pat. Nos. 3,537,893; 3,582,350; 3,443,990 and 4,260,642. The effect of surfactants on starch pastes is also described by E. M. Osman in Starch; Chemistry and Technology, Vol. II, Chapter VII, pp. 189-191; Whistler and Paschall Eds., Academic Press, N.Y. (1967).
The term xe2x80x9cheat-moisture treated starchxe2x80x9d is known in the art and is commonly used to refer to a starch which has been subjected to a heat treatment under controlled moisture conditions, the conditions being such that the starch undergoes neither gelatinization (i.e., exhibits no substantial loss of birefringence) or dextrinization. If heat-moisture treated starches are used in hot-water dispersible foodstuffs, dispersion of the mix into boiling water nevertheless results in formation of lumps and agglomerated or coated masses by surface gelatinization wherein a coating barrier forms on the starch preventing further hydration.
A hot or boiling water dispersible starch product that consistently provides a uniform paste having no lumps or agglomerated masses associated therewith is described in U.S. Pat. No. 4,491,483.
The combination of starch and gums or starch, gums and emulsifiers is generally known (see U.S. Pat. Nos. 3,917,875; 4,140,566; 4,081,567; 4,105,461; 4,119,564; 4,120,986; 4,140,808 and 4,192,900). The gums are used as thickeners or stabilizers in these formulations. Nevertheless, food formulators prefer to use as much starch as possible in these products due to the high cost of gums.
Methods of modifying starch and blends of starch and gums using extrusion are known. U.S. Pat. No. 4,859,484 describes a method of processing starch and gum blends wherein the starch and gum are separately hydrated, intimately commingled and extruded. The method requires water in the amount of 70-200% based on starch weight. Two other U.S. Pat. Nos. 5,208,061 and 5,275,774, describe extrusion methods for making starch products. The use of extrusion to modify starch also has been described by Shaw S. Wang in xe2x80x9cGelatinization and Melting of Starch and Tribochemistry in Extrusionxe2x80x9d, Starch/Starke 45 (1993) Nr.11, pp 388-390.
Applicants have now discovered an improved method of physically modifying starches and mixtures of starches and other materials using pressure and heat, such as by extrusion under specified conditions of moisture, temperature and pressure. The physically modified products of the improved method can be made for high dispersibility in hot or cold liquids and do not form agglomerated masses.
Physically modified starch products having improved functionality in food applications are prepared by extruding starch or mixtures of starch and gum, starch and surfactant, or starch, gum and surfactant. An unmodified starch from one farinaceous material or combinations of unmodified starches from different farinaceous materials and/or a modified starch or starches (such as chemically, genetically or physically modified starches) can be employed as the starting material starch. When gum is mixed with the starting material starch, one or a combination of gums can be used. A surfactant which can be one or a combination of surfactants is added to the starting material starch or starch/gum mixture when a modified starch-surfactant product is desired. The term starting materials as it is used herein means starting material starch, or a mixture of starting material starch and gum, or a mixture of starting material starch, gum and surfactant, or a mixture of starting material starch and surfactant.
The properties of the products of the invention are manipulated by controlling the conditions of extrusion such as the moisture content of the material in the extruder and the die plate temperature and pressure of the extruder.
Known equipment for modifying starches other than extruders can be employed to make the products of the invention and such equipment includes spray dryers, roll dryers, compacting rolls, mills, explosion puffers and other means which allow the operator to control the pressure (or shear), temperature and moisture of the starting materials so that the desired product properties can be obtained.
When mixtures of more than one starch, or starting material starch with other components such as gum and/or surfactant, are employed, the mixtures can be prepared partially or completely before they are added to the extruder or they can be prepared by mixing in the extruder itself. The terms mixture, admixture, blend and the like are used interchangeably in this specification.
The products can be used in many applications calling for modified starch, including food applications such as dry gravy/sauce mixes, (i.e. spaghetti sauce, turkey gravy, hollandaise sauce), salad dressings (pourable and spoonable), instantized starch (for home use), pudding mixes, soup and carriers for dough conditioner, (baking). The products of the invention also exhibit desirable viscoelastic properties (characteristics that are related to desired mouthfeel that are associated with fat mimetic materials).
The extruder is operated with the objective of providing controlled mixing of starch granules such that the end product is a heterogeneous mass of gelatinized, partially gelatinized and ungelatinized starch granules as indicated by photomicrographs. The extruder also is operated with the objective of maximizing mechanical energy levels while minimizing thermal energy input. A screw element configuration for the extruder is selected with the goal of using enough mixing elements at the discharge end to keep the pressure in the barrel as high as possible over a short distance. Moisture content of the starting materials is adjusted by adding water prior to introducing the starting materials into the extruder and/or by water injection into a first section of the extruder barrel at or near the inlet for the starting materials. A die, having a variable orifice or a preselected fixed orifice, is used as a means to control the die-plate pressure within a predetermined range. Pressure and temperature at the die-plate also are a function of the screw configuration and rotational screw speed (revolutions per minute), the rate of feed into the extruder and the composition of the material in the extruder. Temperature is also a function of any cooling or heating added by means of a barrel jacket. When the product exits the die orifice(s) of the extruder, water flashes off as steam, thus reducing the moisture content of the extrudate.
A characteristic of the process is that it requires minimal external temperature control of the type provided by heating and/or cooling jackets surrounding the extruder barrel and in some cases sufficient heat is provided by shearing within the extruder barrel so that no external heat is needed. The ingredients preferably are added to the extruder at ambient temperatures although pre-heating or pre-cooling of the starting materials and/or added water can be used as a means of achieving desired temperatures within the extruder.
The products of the invention can be dried and/or ground or milled provided that the conditions of drying, grinding or milling are selected so as to avoid further gelatinization and loss of functionality of the product. Accordingly, it is preferable to dry at temperatures of about 120xc2x0 F. or less and employ multiple pass grinding or milling to avoid overheating. Conventional dryers such as belt dryers, tube and pneumatic tube dryers, toroidal dryers and flash dryers can be employed. Conventional grinding or milling equipment also can be employed such as a Fitz comminuting machine.
The invention also relates to a unique agglomeration procedure which can be used to enhance the dispersibility of the products in hot systems.
All percentages set forth herein are by weight and all ratios are expressed in terms of weight/weight unless otherwise designated. All references to the weight of starch, starting material starch or starting materials herein include the moisture present therein.